In the reduction of carboxylic acids and esters to aldehydes, some of the known processes and catalysts are as follows:
Strojny, U.S. Pat. No. 4,328,373, describes the reduction of carboxylic acids or esters to aldehydes using catalysts comprised of oxides of yttrium, cerium, praseodymium, zirconium, thorium, uranium, the lanthanides and actinides or mixtures thereof.
U.S. Pat. No. 4,613,700, Maki et al, reports the catalytic hydrogenation of aromatic carboxylic acids to aldehydes using a zirconium oxide catalyst mixed with manganese, bismuth, chromium, cobalt, iron, zinc, lead, rhenium, indium or elements of Group III in periods 3 to 6 of the periodic chart, as well as lanthanoids such as lanthanum, cerium, praseodymium, neodymium, etc.
U.S. Pat. No. 3,517,066, Gurien et al teaches an improved Rosenmund process for reducing a carbonyl chloride to an aldehyde using a metal catalyst comprised of palladium, osmium, platinum, nickel and a salt of a weak acid and a strong base.
Gelbein et al, U.S. Pat. No. 4,585,899, shows a process for hydrogenation of an aromatic or aliphatic carboxylic acid or ester thereof to the corresponding aldehyde in the presence of a manganese dioxide catalyst supported on activated alumina.
Holy et al, U.S. Pat. No. 4,585,900, teaches a process for hydrogenation of an aromatic or aliphatic carboxylic acid or ester to the corresponding aldehyde using a yttrium catalyst activated with copper.